INTRODUCTION: Blood flow distribution after ascending-to-descending aortic bypass in complex aortic arch obstruction is poorly described.

OBJECTIVE: To study blood flow by magnetic resonance (MR) imaging at rest and during exercise in patients with aortic arch obstruction and a bypass tube and in healthy controls.

MATERIAL AND METHODS: Seven patients (median 18 years (range: 14-54 years) and weight 79 kg (range 51-91 kg)) were studied 25 months (range 6-68 months) following surgical insertion of 14- or 16-mm bypass tube from the ascending to the distal descending thoracic aorta. Seven sex- and aged-matched normotensive subjects served as controls. MR real-time flow was measured in the ascending aorta and the proximal descending thoracic aorta in all participants and in the bypass tube in patients at rest and during supine leg exercise at 0.5 and 1.0 W kg(-1).

RESULTS: Ascending aortic flow at rest in patients was 2.9l min(-1)m(-2) (range 2.3-4.4) and increased with exercise to 5.3 (range 4.3-7.3) at 1.0 W kg(-1), which was not different from controls (3.4 (range 2.4-4.6) and 6.1 (range 5.0-6.9)). The bypass tube carried roughly the same flow as the proximal descending aorta at rest (1.5 (range 0.7-2.0) and 1.0 (range 0.2-2.0), respectively, and flows increased similarly during exercise (2.8 (range 1.5-4.0) and 2.0 (range 0.8-4.1), respectively at 1.0 W kg(-1)). Flow to the upper body did not differ between groups nor changed with supine leg exercise.

CONCLUSION: With aortic arch obstruction, an ascending-to-descending aortic bypass tube provides normal flow to the lower body at rest and during supine leg exercise without evidence of steal from the upper body.